Mobile wireless devices, such as cellular telephones, are widely used. In addition to allowing users to carry on voice telephone calls, mobile wireless devices allow users to access data services through which users can obtain many forms of digital content. Users may surf the Internet, download video clips or send electronic messages, to name a few of the possible uses of mobile wireless devices.
Frequently, mobile wireless devices connect to data sources through cellular networks. The cellular networks include base stations distributed throughout an area in which cellular service is provided. In urban areas, the base stations may be spaced by about 300 meters. In rural areas, the base stations may be spaced by a distance of between about 1.5 and 2 Kilometers. Regardless of the spacing, the geographic regions around the base stations define “cells,” with mobile devices in each cell connecting to the base station in that cell.
A mobile device, to connect to a data source, first makes a connection to a base station in its cell. The base station provides access to a network, such as the Internet, over which the mobile wireless device can then access data sources that are also coupled to the network. As mobile devices move from one cell to another, the base stations in those cells communicate to “handover” responsibility for continuing communication with the mobile device, such that communication is not lost even as the mobile device move out of the cell.
To support download of digital content and a growing number of other services, cellular networks have been upgraded to support higher bandwidth communications. State of the art networks communicating using a 3G wireless standard can support data communications at rates in excess of 1 Megabit per second (Mbps). However, it has been found that when many users are in the same cell—such as may occur in an urban area—a base station may become overloaded.
Overload can occur if the cumulative bandwidth that would be consumed if all of the devices communicated at the maximum data rate of the 3G service exceeds the capacity of the base station. When the base station is overloaded, each device is only able to communicate at a fraction of the rated bandwidth of the cellular service or admission to the network is rejected, causing frustration to the user. There are also common situations when mobile devices are at the edge of coverage of a cell where either less spectrum is available (such was mentioned earlier) or there is enough spectrum but providing broadband data requires high transmitted power. This is particularly problematic for portable devices (slate, Netbook, or a smart phone) where even 2 Mbps can drain the battery in less than 30 minutes at the edge of coverage. The same problem arises in building with link loss of 15 dB or higher; this can easily occur in buildings with metal tinted glass windows if devices are even a few meters away from the window, for instance.